1. Field of the Invention
This invention relates to an alternating current generator used for a vehicle or the like.
2. Description of Related Art
FIG. 1 is a sectional view showing the construction of a conventional alternating current generator for a vehicle. In the figure, reference numerals 1 and 2 indicate first and second bowl-shaped housing covers arranged with concave sides facing each other, and serving to house the main part of the alternating current generator. The second cover 2 corresponds to the rear side of the AC generator and has a deeper bowl than the first housing cover 1, which corresponds to the front side of the generator. The first and second covers 1 and 2 house a stator 3 with a ring shaped stator core 3a around which is wound a stator coil along the outer periphery thereof. The first and second covers 1, 2 are tightened by a bolt 19.
At the positions corresponding to the respective bowl bottoms of the first and second covers 1, 2, (i.e., in the axial center of the front and rear sides of the generator), circular bearing boxes 1a and 2a are respectively provided. Bearings 4 and 5 are respectively fitted into the bearing boxes 1a and 2a. The bearings 4 and 5, rotatably support the shaft 6.
A set of pole cores 7 and 8 having opposite polarity are fixed around the shaft 6. Pole cores 7, 8 each have a plurality of axially-projecting wedge-shaped magnetic pole pieces circumferentially formed around discs that are coaxially fixed to shaft 6. The pole pieces of the respective pole cores 7 and 8 are arranged so as to interlace each other. That is, the pole pieces of pole core 7 alternately interface with the pole pieces of pole core 8. An excitation coil 9 is fixed around the shaft 6 between the pole cores 7 and 8. In order to draw external air into the inside of the generator housing, internal fans 10a, 10b which rotate unitedly with the shaft 6 are respectively attached on the front and rear surfaces of pole covers 7 and 8, with the fan blade tips flaring outward from the pole cores. Along the rear portion of shaft 6, at the second cover 2 side, two slip rings 12 made of a metallic conduit are fitted, but are insulated from the shaft 6. A rotor 11 is made up of the shaft 6, pole cores 7, 8, exciting coil 9, fans 10a, 10b, and slip rings 12. The rotor 11 is provided inside the inner peripheral of the aforementioned stator 3.
Inside of the second cover 2, there is housed an electric current supplying unit 13 with brushes 13a, which are slidably connected to the slip rings 12, respectively, for giving exciting current to the exciting coil 9, a rectifier for rectifying induced alternating current by the stator coil 3b into direct current, and a voltage regulator 15 for detecting direct current to control the exciting current to the excitation coil 9 to regulate the output voltage to the battery to a constant level.
On the first cover 1, there are provided at least one inlet hole 101 for drawing outside air to the inside by the rotation of the fan 10a, and at least one discharge hole 102 for discharging the air which has circulated through the inside. On the second cover 2 housing the rectifier 14 and the electric current supplying unit 13, there are provided at least one inlet hole 201 for drawing outside air to the inside by the rotation of the fan 10b, and at least one discharge hole 202 for discharging the air which has passed through the inside.
Around the end of the shaft 6 on the first cover 1 side, in the vicinity of the outer surface of the cover 1 is fixed a single groove pulley 16 which transmits the rotational power of an engine to the shaft 6. Around the end portion of the shaft 6 on the second cover 2 side, in the vicinity of the outer side surface of the second cover 2, is fixed a single-groove pulley 17 which transmits this rotational power to an auxiliary machine. The outer peripheral edge of the pulley 17 reaches the position corresponding to the inlet holes(s) 201 of the second cover 2.
Explanation will be given on how the conventional alternating current generator of the above construction operates to cool the inside thereof. The rotation of the engine is transmitted through the pulley 16 to rotate the shaft 6. When the shaft 6 rotates, the internal fans 10a, 10b fixed on both outer surfaces of the rotor 11 rotate. By the rotation of the fans 10a, 10b, relatively cold outside air is drawn in through both first and second covers (1 and 2) via the inlet holes (101, 201, respectively), to the inside. The air then passes through the inside as shown by the arrows a and b in the figure cooling the generator components as it circulates therethrough.
The drawn air shown by the arrow a is discharged from the discharge hole 102 after cooling the bearing 4, pole core 7, excitation coil 9, and stator coil 3b. The drawn air shown by the arrow b is discharged through the discharge hole 202 after cooling the voltage regulator 15 and the rectifier 14, and further, the pole core 8, excitation coil 9, and stator coil 3b.
Since the outer peripheral edge of the pulley 17 reaches the radial position corresponding to the inlet hole 201, however, the outside air drawn into the inlet hole 201 is that outside air which had circulated along the outer surface of the second cover 2 as indicated by an arrow b' in the figure. As the temperature of the second cover 2 becomes higher by the heat generated inside, the temperature of the air circulating along the outer surface of the second cover 2 rises by receiving the heat from the second cover 2, thereby resulting in high temperature air being drawn into the inlet hole 201.
Accordingly, a problem arises in sufficiently cooling such components as the rectifier 14 and the voltage regulator 15 by such high temperature air.